1. FIELD OF THE INVENTION
The present invention relates to manufacturing of lens array which is to be used as a lens system of document copier, facsimile, printer, white board scanner and so on.
2. DESCRIPTION OF THE PRIOR ART
As a conventional lens array which is to be used for reading of image data. SELFOC lens array (trade mark of Nippon Sheet Glass Company, Limited) which has arrays of graded index lenses is known and widely used in the art.
Furthermore, a lens array, for example shown in Japanese Published Unexamined Patent Application Sho 53-122426 or Sho 55-83071 is known, wherein rod lens arrays are doubled upper and lower.
In the former case of graded index lens array, it is necessary to make accurate gradation of index of glass in radial direction of the lenses. Therefore, manufacturing system of the graded index lenses is complicated, processing time thereof becomes long and the graded index lens array is expensive.
In the latter case of rod lens array, respective rod lenses are generally formed by compression molding shown in FIGS. 3(A) and 3(B). In FIG. 3(A), a rod 101 of transparent resin is inserted in a die 104 and the die 104 is heated for softening the rod of transparent resin 101. Thereafter, core inserts 102 and 103 respectively having mirror-finished concave surfaces are pressed on the transparent resin rod 101, as shown in FIG. 3(B). Thus, the rod lens 100 is formed. Thereafter, a plurality of the rod lens are inserted in a lens-holding frame of a block plastic mold with great care so as to dispose the rod lenses with high accuracies of optical axes and axial positions.
In such conventional manufacturing of rod lenses, processing time to form the rod lenses are too long to mass-produce. And also, as the lens surface are formed by compression, the lens surfaces may be discrepant from designed curves. Furthermore, the rod lens array must have a process for inserting the rod lenses into through holes of a lens holder precisely. Therefore, the rod lens array is expensive.